The sweep cycle of a beam-deflecting system is divided into a relatively long forward phase, or trace, and a relatively short flyback phase, or retrace. In conventional systems of this type, e.g. as described by M. E. Wilcox in an article entitled "A Complete Monolithic Vertical-Deflection System for Television", IEEE Transactions on Broadcast and Television Receivers, Vol. BTR- 17, No. 4, November 1971, the two phases are produced under the control of a sawtooth oscillator whose output voltage rises progressively from a base level during the trace and drops back to that level during the retrace, the length of the flyback phase being determined by a rectangular pulse emitted by that generator. The flyback is generally accompanied by a blanking of the beam of the cathode-ray tube.
It has already been proposed (see U.S. Pat. No. 3,727,096) to provide capacitive storage means in a scanning circuit of such a deflection system for accumulating some of the yoke energy available during the forward sweep in order to produce a flow of reverse current during flyback. In all these conventional systems, the duration of the flyback phase is controlled by the sawtooth oscillator and cannot be selected independently of other parameters of the sweep cycle.